Length
In geometric measurements, length most commonly refers to the longest of an object.Princeton.edu In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a which is shorter than wire . Another example is s, in which the width may be larger than channel length. Length may be distinguished from , which is vertical extent, and width or breadth, which are the distance from side to side, measuring across the object at right angles to the length. Length is a measure of one dimension, whereas is a measure of two dimensions (length squared) and is a measure of three (length cubed). In most , the unit of length is a , from which other units are defined. History NPL.co.uk Measurement has been important ever since man settled from his nomadic lifestyle and started using building materials; occupying land and trading with his neighbours. As society has become more technologically oriented much higher accuracies of measurement are required in an increasingly diverse set of fields, from micro-electronics to interplanetary ranging. One of the oldest units of length measurement used in the ancient world was the cubit which was the length of the arm from the tip of the finger to the elbow. This could then be subdivided into shorter units like the foot, hand (which at 4 inches is still used today for expressing the height of horses) or finger, or added together to make longer units like the stride. The cubit could vary considerably due to the different sizes of people. After 's , length can no longer be thought of being constant in all reference frames. Thus a ruler that is one meter long in one frame of reference will not be one meter long in a reference frame that is travelling at a velocity relative to the first frame. This means length of an object is variable depending on the observer. Units In the physical sciences and engineering, when one speaks of "units of length", the word "length" is synonymous with " ". There are several that are used to length. may be based on lengths of human body parts, the distance travelled in a number of paces, the distance between landmarks or places on the Earth, or arbitrarily on the length of some fixed object. In the International System of Units (SI), the basic unit of length is the meter and is now defined in terms of the . The and the , derived from the meter, are also commonly used units. In U.S. customary units, English or Imperial system of units, commonly used units of length are the inch, the foot, the yard, and the mile. Units used to denote distances in the vastness of space, as in , are much longer than those typically used on Earth and include the , the , and the . See also * * * * * * * * * * References Category:Measurable quantities